Middleweight Heresy, Redux

Kawasaki 636
Thunderhill, CA
October 10, 2012


Children, with a complete lack of context or perspective, believe that as the world is, so has it always been, so shall it always be. This is true for kids coming of age around the world creating varied expectations be it based on experiences of beach trips or armed conflict.

An existence in the present tense is something we are supposed to out grow as adults and yet while we admonish the next generation to appreciate their advantages (something they are cognitively prohibited from doing) we, ourselves, drift into contempt bred from familiarity. Eloquently stated on the mid 1980s bumper sticker from Alaska “Please God give me another oil boom and this time I won’t piss it away” although one can be fairly certain that IRA deposits are far from the thoughts of the oil frackers in the Dakotas today.

Recreational motorcycle riding has really only been gaining popularity since 1970. Since that time there have been two big retractions, one in the early eighties that created a glut of unsold air-cooled bikes and import tariffs on Japanese bikes. The next one started in 2007. In 2006, Suzuki sold about 20,000 GSX-R 600s. In 2012 they will sell under 4,000.

While wage growth has stalled for decades in the US, the strengthening Yen has doubled the price of a 600 sportbike in the last ten years. The average age for motorcycle riders gets older each year and track days, (which basically didn’t exist twenty years ago,) are populated, predominantly, by men in their forties and fifties. It is entirely possible that motorcycle riding, once the bastion of youthful rebels, will eventually be the cultural equivalent of HAM radio operators.

And so it is easy to forget that the 600cc sportbike class was basically invented by Honda in 1987 and was symbiotically marketed thru the creation of the AMA Supersport racing series to popularize the category. 750s stuck around for another decade until, for all intents and purposes, Suzuki finally shot the entire retail class in the head in 1996 with its unmatchable light weight and very powerful model and unintentionally ended 750s as a popular category when the rest of the manufacturers packed in the 750 class and we were left with 1,000s and 600s. However, these displacement classes are ultimately, arbitrary.

Ten years ago Kawasaki broke with the then orthodoxy of the racing classes and released a stroked version of their 600, creating a displacement of 636. The bikes were virtually identical except for the crank and rods. The 636 was a big seller for Kawsaki from 2002-2006. Then the bottom fell out of the motorcycle market and the 636 was retired from the line up.

Since 2007 the entire motorcycle market has contracted viciously. Suzuki went from selling 20,000 GSX-R 600s a year in 2006 to suspending imports in 2009. Now they hope to sell 3,000 in the US per year.

Kawasaki, remember, mainly builds trains, ships, marine engines, and gas turbine generation plants, although a lot of their profits have been historically derived from their consumer products division. The pressure on the global economy has been even more cruel on the rest of their divisions so, in response, the motorcycles have increased in relevance for the corporation.

Perhaps with a tinge of nostalgia for the good old days of healthy 636 sales, Kawasaki has brought the model back,. However, this time they have not just tossed a stroked crank into their 600, they really built a whole new engine and wrapped it in distinctive bodywork.

Track day ready, right out of the crate.


Also, shockingly on its face, they abandoned their 600 in the US for the 2013 model year.

Dissecting that dynamic a little reveals more about the frailties of racing and market than the strength of their product line. Kawasaki will still be selling their 600 along side the 636 in Europe in 2013. Kawasaki won the World Supersport title in 2013 and came within a hair's breadth of winning the World Superbike title with the similarly styled ZX10. Kawasaki has a very high profile in middleweights in Europe, while in the US, they have largely ceded that profile to Yamaha and Suzuki by deciding to sit out the national race series for the last three years. And thus, Kawasaki probably has a lot of unsold 2012 600 inventory sitting in dealers and in the warehouse and so they don’t need to go through the importation hassles of importing more 600s for 2013.

I was invited to California to Thunderhill Raceway to test the new 636. Thunderhill is a really nice circuit. It has a lot of flowing, predominantly left, sweepers with a few dramatic topography changes thrown in to keep it interesting. There is also a double apex flat camber second gear right hander which craves lean angle.

Lightweight + Natural Geometry = Perfect Apexing


The 636 handled it all with aplomb. The bike ships with Bridgestone S20s, (an excellent street tire,) although we were running R10 Evos (a Bridgestone race tire) on the track. We had tire warmers and 30 minute sessions which new tires every 90 minutes. As such, we got close to, but not actually at, the point of wearing out the rears.

The older ZX-6 had a noise canceling butterfly in the under seat exhaust
pipe, the new 636 has packed a massive amount of exhaust volume into
the headers, the collector and the muffler. Also notice the massive radiator
lurking in the shadows.


With all of the balanced engine tuning, the bike makes huge torque for a middleweight. Some 600s really need to have their nuts wrung to get moving,; this one you can decide to lug on the torque or scream on the horsepower. That flexibility, as well as perfect fueling, makes for a very forgiving engine., an indulgence that I welcomed as I felt my way around the unfamiliar track.

I did three race launches pulling out onto the track. The clutch had smooth engagement with no judder or shudder. The trick lock up clutch (more on that later) seemed to be everything that they intended it to be.

The brakes had a little bit of that “in the pits radial brake mushiness” feel but they tightened right up once back on the track. They were very good brakes. , offering linear feel with plenty of power allowing for both fork- crushing stopping power as well as trail braking sensitivity.

The bike steered very well but, despite the lack of a steering damper, was still stable even when cresting a third gear hill with a little lean angle and the front tire floating slightly off the ground. The bike was also predictable and responsive through the aforementioned double apex right allowing for serious lean angle and effortless carving.

Once I had learned the track a bit and started riding with more aggression I noticed that the depressions in the track in some of the corner apexes were gravity-loading the suspension beyond its comfort limits. This was at a pretty quick clip but it made me want both the front and the rear suspension action slowed down a bit, as well as more spring in the front. Curtis Adams (yes, racing legend Curtis Adams) is now one of Kawasaki's test riders and was my tech for the day, and he obliged by adding some preload, and a shade of rebound to the shock, and more compression and rebound damping to the forks. This all helped settle the bike more in the fourth gear G out conditions.

The upper shock mount has the capacity to accept these cute Kawasaki slide in shims to raise or lower the rear ride height. I think if I had a 636 track bike, and I was on a budget, I would try replacing the .875 fork springs with .925 (I weigh 165 BTW) and measuring how much higher that made the front end sit. Then I would shim the shock to keep the same balance, keeping in mind that the effect of the spacers gets multiplied through the linkage so you have to measure at the axle. This should not be taken as a criticism of the stock set up; it's just with such a capable bike, great tires and a compelling race track, it's tough to not day dream about starting grids.

The transmission, a trouble spot for some Kawasaki’s of the past, was flawless. It doesn't have a quick shifter but with three hours of track time (which is a lot of track time) I didn’t miss or hang a single shifter with simple old school speed shifting.

My one pet peeve about the ergonomics would be that there is a slight space on the right footpeg between the peg and the ankle guard which would catch the toe of my boot, making it a shade dicey once in a while in the fast left right of the famous Thunderhill corkscrew.

After three hours the bike still felt like it was steering fast, braking hard and pulling strong.

The next day we took a little 84 mile street ride on an amazing curvy road. There is a painful truth that the better a bike is for the track, the worse it is for the street. This street ride was a bit of a cherry pick since we were bused for the hour of boring flat straight road and only rode on curves. Riding at an ill advised criminal pace which would lead to incarceration or serious injury if done over a period of weekends, I was still well inside the limits of the bike. Meaning, the risks were dogs, deer, gravel, diesel spills, trucks crossing the center line or other riders making mistakes, not any limitation of the 636.

If you have to commute on your track bike, this will work better than some of the more highly strung 600s out there. You can ride this on the street and, actually, its suspension and motor are pretty civilized for doing just that; however, spiritually and ergonomically it is sheer torture to ride a sport bike (not just this one) on the street. It’s not like a lot of people drive around in open wheeled street cars just because they like F1.

It steers, shifts, accelerates and brakes like a tight responsive track bike should but since it is almost impossible to tax the bike on the street, it was also a little tedious. As any good track bike should, it forces the rider to carry a lot of weight on the wrists and the unrelenting riding positions slowly put my hands to sleep. The bike was bored and agitated and impatient at anything less than an 9/10th pace. It was very polite in its protestations and didn’t buck or overheat, but the bike clearly wanted to get off the highway and back to Thunderhill.

The shifter can be flipped without drama and
the bike ships stock with a light 520 chain.


So what do you get for your $11,699?

The 636 was stroked 2.6mm to increase displacement. However, this time Kawasaki made multiple other changes to the engine and bike. For price point they dropped four injectors, leaving four slightly nicer ones to handle fueling. They increased the size of the ports in the head and moved the water jackets to accommodate the new port sizes.

Slightly bigger cams extended the duration by 3 degrees on the intake but, more importantly, increased lift from 8.6mm to 8.8mm on the intake and from 7.2mm to 7.4mm on exhaust. All things being equal, more lift is good for midrange power, more duration is good for top end power. The lift increase here compliments the stroke to boost the area under the curve and make more power available at all RPMs, not just when the engine is screaming, which, even in racing, is only a small percent of the time. The exhaust pipe received a cross tube to connect all header pipes, also to compliment mid-range power.

Strangely, the compression ratio, which is normally raised through stroking, was lowered from 13:1 to 12.9:1 but, at those high compression levels, in the opinion of this moto-journalist, such a change is not significant.

To accommodate the higher piston speeds brought about by the longer stroke, the wrist pins have been beefed up to handle the extra forces and the connecting rods have been made 2mm wider. Kawasaki even had to make new cases for the 636 because they needed to relocate the windage ventilation holes in the crank cases.

The 636 got a new fairing to imitate its famous sibling and an 11% larger airbox to both contribute to power output and take up the space that was freed by the loss of one set of injectors.

All that is claimed by Kawasaki to knock .2 seconds off its quarter mile time compared to the 2012 600.

So far these are all pretty standard engine tuning tricks. One neat innovation is the new F.C.C. clutch. The clutch's engagement ramps are, by my eye, about 25mm long. However, the clutch has ramps which go both directions. That means that, under deceleration the clutch slips and, under acceleration, the clutch clamps harder. This acceleration clutching multiplier allowed Kawasaki to use a smaller clutch and only three clutch springs instead of the more typical five or six. The result is a 700 gram lighter clutch pack. Keep in mind, that the clutch spins really fast so that 700 fewer grams will result in faster acceleration and, less obviously, better handling. Kawasaki famously put in a 2 X engine speed alternator a few years back in their 1000 that that made for some really weird handling characteristics so don’t discount handling improvements from lighter engine rotating pieces.

Although the 636 has a cassette transmission which allows for easy servicing, it also got thicker gears to be able to withstand the increase in power. First gear was shortened a tad as well while the rest of the gear box ratios were left intact.

Kawasaki loaded the bike up with various power modes and traction control. I still have not been able to figure out who all the customers are that want a “low” power mode on their sport bikes but, if you want it, the 636 has it. The 636 also has the S-KTRC for traction control with four settings between off – 1 – 2 – 3 in increasing application of throttle control.

Honestly, with modern 180 tires one would be hard pressed to get this thing into a traction controlled situation unless the tire was wearing out, the rider was ridiculously optimistic about lean angle and throttle application, or the surface was compromised. That said, like alibis, cash, condoms, passports, lawyers, broad spectrum antibiotics or guns, it is nicer to have it and not need it than it is to need it and not have it.

The chassis received a bit of attention as well. Although the frame, subframe and swingarm are all virtually the same, they were tweaked a bit to be able to mount the new bodywork.

Perfect fueling and linear mid range power
delivery encourages early throttle application


The fork tubes are now set in the triple trees 2mm higher, (decreasing trail and rake,) while the back end has been raised slightly. This bumps the rake down from 24 to 23.5 and makes for a more nimble ride. Ultimately taking out trail will also make the bike a little vague in ultra high speed sweepers but anyone who has got the wherewithal to go fast enough to notice that will have already changed the suspension and geometry in a radical fashion.

The 636 receives Showa’s latest fancy fork which has some claimed benefits of more sensitivity and simpler adjustments , and, although it worked well enough, I am not quite sold on the concept. The forks have a Separate Fork Function and a Big Piston making it a SFF-BP. Both forks have a spring in them but the preload is only adjustable on one leg while the damping is controlled in the other. The piston is a big ass piston at 37.6mm which should make it very sensitive, in a good way, in the initial stroke. The tube walls are a little thinner as well knocking 220g off the weight.

The business end of the Showa Separate Fork Function- Big Piston front
The inconveniently unconventional fastener on the left is for adjusting
preload and the two adjusters on the right are for adjusting damping.


The shock has a lighter and slightly longer spring to make it more plush over bumps.

The front wheel speed sensor is overshadowed by the Nissin
monobloc calipers gripping wafer thin front rotors.


The brakes are Nissin monobloc calipers which are more rigid than the 2012’s, and the rotors grew from 300mm to 310mm to save weight and thinned down from 6.0mm to 5.0mm. The last time I saw 5.0mm front rotors on a sportbike was the 1996 GSX-R 750. Those proved a little too thin and were bumped up to 5.5 for the next year. Perhaps metallurgy has improved in the last decade or perhaps 636 track riders will be buying a lot of rotors. The new calipers have four 32mm pistons instead of the usual staggered pistons typically employed to provide balanced pad wear. ABS is also available as an option.

A hint more stroke and a tad more bore and the world
could welcome back the 750 class.


The 636 received new styling to more closely resemble the ZX-10 and is available in black, white and, of course, green.